Genetics of Galactosemia​A person unaffected by galactosemia (neither carrier nor galactosemic) inherits two ‘normal' genes for the production of the GALT enzyme (the enzyme needed to convert galactose into a form usable by the body) . This person's genotype would be N/N and their enzyme activity would be normal.

A person who is a carrier of classic galactosemia inherits one normal gene from one parent and one gene containing the error that leads to classic galactosemia from the other parent. This person's genotype would be G/N and their enzyme activity would be less than normal, but not so much so as to cause medical complications or require dietary management.

A person who is classic galactosemic inherits two genes with the error, one from each of his/her parents. This person's genotype would be G/G and their enzyme activity would be essentially zero.

History of GalactosemiaGalactosemia was first "discovered" in 1908. Von Ruess, in a 1908 publication entitled, "Sugar Excretion in Infancy," reported on a breast-fed infant with failure to thrive, enlargement of the liver and spleen, and "galactosuria". This infant ceased to excrete galactose through the urine when milk products were removed from the diet. The infant, however, later died because of other complications (the baby had been given tea laced with cognac as treatment as well). An autopsy revealed cirrhosis of the liver, which they thought was due to the infant's alcohol ingestion. Though confirmation of the diagnosis was not possible at that time, it has been generally accepted that Von Ruess was the first to report on a patient with galactosemia. http://www.galactosemia.org/history-of-galactosemia/

The disease was first recognized and described in detail (ie published work) in 1935 by Mason and Turner. Leloir worked out the metabolic pathway and the process of sugar-nucleotides and won the Nobel prize in Chemistry in 1970 for his work. He and coworkers elucidated the pathway for converting galactose to glucose in the early 50's.

Although, the clinicians recognized galactosemia very early in the century, the defective gene that caused it wasn't found until 1956. Another major break-through was when it was first found to be detectable through a newborn screening method in 1963. This method was developed by Guthrie and Paigen. Galactosemia was the second disorder found to be detectable through newborn screening methods by Robert Guthrie www.nbstrn.org/about/spotlight/Guthrie

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